Optical switch using micro-electromechanical system

ABSTRACT

Provided is a 2×2 optical switch includes a substrate, a first input fiber and a first output fiber, a second input fiber and a second output fiber, a rotating mirror, torsion bars, and an electrostatic force generating part. The first input fiber and a first output fiber are arranged at a predetermined distance from a central point in a first optical path passing through the central point over the substrate. The second input fiber and a second output fiber are arranged at a predetermined distance from the central point in a second optical path that passes through the central point and is orthogonal to the first optical path. The rotating mirror is positioned at around the central point and turns on a turning shaft. The torsion bars support the rotating mirror and the electrostatic force generating part supplies a drive force to the rotating mirror.

BACKGROUND OF THE INVENTION

This application claims the priority of Korean Patent Application No.2003-3667, filed on Jan. 20, 2003, in the Korean Intellectual PropertyOffice, the disclosure of which is incorporated herein in its entiretyby reference.

1. Field of the Invention

The present invention relates to an optical switch using amicro-electromechanical system (MEMS), and more particularly, to a 2×2way optical switch.

2. Description of the Related Art

U.S. Pat. Nos. 6,303,885, 6,315,462, and 6,229,640 disclose techniquesfor a 2×2 way optical switch used in various optical applications.Optical switches disclosed in U.S. Pat. Nos. 6,229,640 and 6,315,462have a structure in which a mirror is driven by an electro-static combdrive and the optical switch disclosed in U.S. Pat. No. 6,303,885 has astructure in which a mirror is driven by spring arms. The structures ofthe optical switches have a common feature in that the mirror moves inparallel with the plane of a substrate by an actuator.

FIG. 1 is a microscopic photo of a conventional 2×2 comb drive opticalswitch having two inputs and two outputs, and FIG. 2 is a plane view ofa portion marked with dotted lines in FIG. 1 to explain the conventional2×2 comb drive optical switch shown in FIG. 1.

As shown in FIGS. 1 and 2, first and second optical input fibers 2 a and2 b, and first and second optical output fibers 3 a and 3 b are arrangedat around the central point P at an angle of 90 degrees. A mirror 1 ispositioned at the central point P of the first and second optical inputand output fibers 2 a, 2 b, 3 a, and 3 b.

As shown in FIG. 3, when the mirror 1 is positioned out of the centralpoint P, optical signals incident through the first and second inputfibers 2 a and 2 b proceed toward the first and second output fibers 3 aand 3 b on the same axes with the first and second input fibers 2 a and2 b without being reflected.

As can be seen in FIG. 4, when the mirror 1 is positioned at the centralpoint P, an optical signal incident through the first input fiber 2 a isreflected from one side of the mirror 1 and then proceeds toward thesecond output fiber 3 b, and an optical signal incident through thesecond input fiber 2 b is reflected from the other side of the mirror 1and then proceeds toward the first output fiber 3 a.

Here, as shown in FIG. 4, when an optical signal is reflected by amirror, the optical signal is reflected out of the central point of themirror. Thus, the reflected optical signal does not proceed toward thecentral point of a target fiber. This is caused by an offset of anoptical path due to the thickness of the mirror.

The offset causes light loss. The thicker the mirror, the greater theoffset, which increases light loss. Accordingly, the thickness of themirror is required to be reduced as it can be in order to reduce theoffset of an optical path changed by the mirror. However, since in theabove-described comb drive optical switch, the mirror moves in parallelwith the plane of the substrate and a reflective surface of the mirroris perpendicular to the plane of the substrate, there is a limitation inreducing the thickness of the mirror. In particular, when forming amirror, silicon is vertically etched in a plasma process, and then ametal having a high reflectance is deposited on the surface of theresultant structure. Thus, it is difficult to reduce the thickness ofthe mirror. Also, since the vertically etched surface is used as areflective surface, a large amount of light is lost when light isreflected. Furthermore, since a high-priced silicon on insulator (SOI)wafer not a general wafer is used, cost for manufacturing the mirror ishigh.

SUMMARY OF THE INVENTION

The present invention provides an optical switch capable of reducing anoffset of an optical path by reducing the thickness of a mirror.

The present invention also provides an optical switch which can cause asmall amount of light loss and be manufactured at a low cost.

According to an aspect of the present invention, there is provided anoptical switch including a substrate, a first input fiber and a firstoutput fiber, a second input fiber and a second output fiber, a rotatingmirror, torsion bars, and an electrostatic force generating part. Thefirst input fiber and a first output fiber are arranged at apredetermined distance from a central point in a first optical pathpassing through the central point over the substrate. The second inputfiber and a second output fiber are arranged at a predetermined distancefrom the central point in a second optical path that passes through thecentral point and is orthogonal to the first optical path. The rotatingmirror is positioned at around the central point and turns on a turningshaft extending in parallel with the substrate. The torsion bars supportthe rotating mirror so that the rotating mirror rotates. Theelectrostatic force generating part supplies a drive force to therotating mirror.

In an aspect of the invention, trenches into which the first and secondinput fibers and the first and second output fibers are inserted areformed in the substrate along the first and second optical paths.

In an exemplary embodiment of the invention, the rotating mirror has afirst position where the rotating mirror is parallel with the substrateand a second position where the rotating mirror is perpendicular to thesubstrate, and turns from the first position to the second position bythe electrostatic force generating part.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present inventionwill become more apparent by describing in detail exemplary embodimentsthereof with reference to the attached drawings in which:

FIG. 1 is microscopic photo of a conventional optical switch including amirror perpendicular to a substrate;

FIGS. 2 through 4 are views for illustrating an optical path changed bythe conventional optical switch shown in FIG. 1;

FIG. 5 is a schematic plane view of an optical switch according to thepresent invention;

FIG. 6 is a perspective view of a mirror and a mirror driving actuatorused in the optical switch according to the present invention;

FIG. 7 is a schematic cross-sectional view of the mirror drivingactuator shown in FIG. 6;

FIG. 8 is a cross-sectional view taken along line I—I of in FIG. 5;

FIG. 9A is a cross-sectional view of a trench into which an opticalfiber is fixed, in the optical switch, according to the presentinvention, shown in FIG. 5;

FIG. 9B is a plan view of a spring formed in an opening of a trench intowhich an optical fiber is fixed in the optical switch according to anexemplary embodiment of the present invention;

FIG. 10 is a schematic cross-sectional view for explaining a process ofinserting an optical fiber into a trench in the optical switch accordingto the present invention;

FIGS. 11A and 11B are views for explaining the operation of the opticalswitch according to the present invention; and

FIGS. 12A through 16B are cross-sectional views for explaining a methodof manufacturing the optical switch according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, an optical switch according to an exemplary embodiment ofthe present invention will be described in detail with reference to theattached drawings.

As shown in FIG. 5, optical input fibers 20 a and 20 b, and opticaloutput fibers 30 a and 30 b are arranged at around the central point Pat an angle of about 90 degrees. A rotating mirror 10 is positioned atthe central point P. As in a general optical switch, the optical inputfibers 20 a and 20 b, and the optical output fibers 30 a and 30 b areinserted into trenches 41 formed in a substrate 40. The trenches 41 arearranged at around or at about the central point P at an angle of about90°. As shown in FIG. 6, the rotating mirror 10 is fixed to posts 42formed on the substrate 40 and supported by torsion bars 43 that extendfrom the posts 42 in parallel with the substrate 40. The torsion bars 43support the rotating mirror 10 so that the rotating mirror 10 isparallel with the substrate 40. When the rotating mirror 10 turns due toan electrostatic force, the torsion bars 43 provide a returning force tothe rotating mirror 10 so that the rotating mirror 10 returns to theoriginal position. The torsion bars 43 extend toward a turning axis X—Xat an angle of approximately 45 degrees with the optical input fibers 20a and 20 b and the optical output fibers 30 a and 30 b. A well 45 isformed under the rotating mirror 10. The well 45 has a rectangular shapeand a vertical sidewall 44 contacting one side of the rotating mirror 10when the rotating mirror 10 turns due to an electrostatic force.

FIG. 7 shows the cross-section of the well 45 and the rotating mirror10. Referring to FIG. 7, a fixed electrode 46, which is opposite to therotating mirror 10 when the rotating mirror 10 faces the verticalsidewall 44, is formed on the vertical sidewall 44. The fixed electrode46 extends to the bottom of the well 45. A dielectric or insulatinglayer 47, which serves to prevent the direct contact of the rotatingmirror 10 with the fixed electrode 46, is formed on the fixed electrode46. The rotating mirror 10 is formed of a conductive material, e.g., ametal thin film, and has reflective surfaces on either side thereof.Thus, when the rotating mirror 10 is substantially parallel with thesubstrate 40 as indicated by “A”, the rotating mirror 10 passes a beamso as to optically connect the fibers facing on the same axis, and whenthe rotating mirror 10 is substantially perpendicular to the substrate40 as indicated by “B”, the rotating mirror 10 reflects an incident beamso as to change the optical path of the incident beam. According to anexemplary embodiment of the present invention, an anti-electrostaticelectrode 48, which maintains the same potential as the rotating mirror10, is formed under the rotating mirror 10 and on an opposite side ofthe well 45 centering at around the posts 42. This is to prevent anelectrostatic force from being generated between the rotating mirror 10and the vertical sidewall 44 of the well 45 so that an attractive forceis generated only in the well 45 due to the electrostatic force.

FIG. 8 is a cross-sectional view taken along line I—I of FIG. 5.Referring to FIG. 8, an insulating layer 49 is formed at around thecentral area in which the rotating mirror 10 is positioned. A metallayer 50 is formed on the insulating layer 49. The metal layer 50 isformed from the same material the rotating mirror 10 is formed from, atthe same time, and then separated from the rotating mirror 10 during apatterning process of a process of manufacturing the rotating mirror 10.The insulating layer 49 is a sacrificial layer necessary for forming therotating mirror 10 and the posts 42, serves as a layer on which a metalthin film is deposited to form the rotating mirror 10, and is locallyremoved after completing the rotating mirror 10.

FIG. 9A is a cross-sectional view showing the internal structure of thetrenches to which the optical input fibers 20 a and 20 b and the outputfibers 30 a and 30 b are fixed. Referring to FIG. 9, a portion of theinsulating layer 49 and a portion of the substrate 40 are etched to formthe trenches 41 into which the optical input fibers 20 a and 20 b andthe output fibers 30 a and 30 b are inserted. Openings of the trenches41 are narrowed by the metal layer 50. Here, a spring 51 of the metallayer 50 restrains the optical input fibers 20 a and 20 b and theoptical output fibers 30 a and 30 b from separating from the trenches41. Referring to FIG. 9B, the spring 51 may be further flexiblycomb-shaped. As shown in FIG. 10, the spring 51 elastically deforms sothat the optical input fibers 20 a and 20 b and the optical outputfibers 30 a and 30 b engage the trenches 41. Channels 41 a are formed toa width smaller than the diameter of the optical input fibers 20 a and20 b and the optical output fibers 30 a and 30 b in the trenches 41 andin the surface of the substrate 40. The channels 41 a support theoptical input fibers 20 a and 20 b and the optical output fibers 30 aand 30 b and determine the positions of the optical input fibers 20 aand 20 b and the optical output fibers 30 a and 30 b.

FIGS. 11A and 11B are views for explaining an optically switching stateby the rotating mirror 10. FIG. 11A shows that an electrostatic force isnot applied to the rotating mirror 10, i.e., the rotating mirror 10 isparallel with the substrate 40 as indicated by “A” in FIG. 7. In thisstate, beams incident through the optical input fibers 20 a and 20 bproceed toward the optical output fibers 30 a and 30 b on the same axesas the optical input fibers 20 a and 20 b, respectively. FIG. 11B showsthat an electrostatic force is applied to the rotating mirror 10, i.e.,the rotating mirror 10 is substantially perpendicular to the substrate40 as indicated by “B” in FIG. 7. In this state, beams incident throughthe optical input fibers 20 a and 20 b are reflected from the rotatingmirror 10 and then proceed toward the optical output fibers 30 b and 30a on the different axes from the optical input fibers 20 a and 20 b,respectively.

As described above, an optical switch according to the present inventionis a 2×2 optical switch in which a moveable electrostatic actuator andoptical fibers are combined. The optical switch has a structure in whicha mirror and the fibers are arranged by a trench structure having aspring.

A process of manufacturing the optical switch of the present inventionhaving the above-described structure will be described in brief withreference to FIGS. 12A through 16B. This process corresponds to awell-known MEMS process, and thus steps of forming detail structureswill be briefly explained herein. FIGS. 12A, 13A, 14A, 15A, and 16A arecross-sectional views for showing a mirror and a well thereunder, andFIGS. 12B, 13B, 14B, 15B, and 16B are cross-sectional views for showingtrenches.

FIGS. 12A and 12B, a well 45 having a vertical sidewall 45 a and achannel 41 a constituting a lower part of the trench 41 into which afiber is inserted are formed in a silicon wafer or a glass substrate 40.A metal layer is deposited and then patterned to form a fixed electrode46 and an anti-electrostatic electrode 48.

As shown FIGS. 13A and 13B, an insulating layer 47 is formed on theentire surface of the glass substrate 40.

As shown in FIGS. 14A and 14B, a film 49 made of an insulator islaminated on the insulating layer 47 on the glass substrate 40.

As shown in FIGS. 15A and 15B, a metal layer 50 is deposited on the film49 and then patterned to form a mirror 10 opposite to the well 45 and aspring 51 that is positioned over the channel 41 a.

As shown in FIG. 6, structures for supporting the mirror 10 and fibersare completed using a dry etching process.

As described above, in an optical switch according to the presentinvention, a mirror can turn at an angle of approximately 90 degrees,which results in adjusting optical paths. In other words, the opticalswitch according to the present invention can be switched by a moveableactuator having a simple structure without using a comb drive linearactuator having a complicated structure. Here, the thickness of themirror is determined when depositing a metal layer. In other words,since the metal layer can be deposited to a thickness of hundreds of Å,the thickness of the mirror can be drastically reduced. The reduction inthe thickness of the mirror means that the light loss due to an offsetin a conventional optical switch can be almost eliminated. Also, sincethe deposited metal layer is used as the mirror, light loss caused bythe roughness of the mirror can greatly be reduced.

The optical switch according to the present invention can bemanufactured using a general wafer unlike existing methods tomanufacture switches from an SOI wafer. Thus, the optical switch can bemanufactured according to a simple unit process, resulting in a greatreduction in cost for manufacturing the optical switch.

While the present invention has been particularly shown and describedwith reference to exemplary embodiments thereof, it will be understoodby those of ordinary skill in the art that various changes in form anddetails may be made therein without departing from the spirit and scopeof the present invention as defined by the following claims.

What is claimed is:
 1. An optical switch comprising: a substrate; afirst input fiber and a first output fiber that are arranged at a firstpredetermined distance from a central point in a first optical pathpassing through the central point over the substrate; a second inputfiber and a second output fiber that are arranged at a secondpredetermined distance from the central point in a second optical paththat passes through the central point; a rotating mirror that ispositioned at around the central point and turns on a turning shaftextending in a direction substantially parallel with the substrate; barsthat support the rotating mirror so that the rotating mirror rotates;and an electrostatic force generating part that supplies a drive forceto the rotating mirror.
 2. The optical switch of claim 1, whereintrenches into which the first and second input fibers and the first andsecond output fibers are inserted are formed in the substrate along thefirst and second optical paths.
 3. The optical switch of claim 2,wherein the rotating mirror has a first position where the rotatingmirror is substantially parallel with the substrate and a secondposition where the rotating mirror is substantially perpendicular to thesubstrate, and turns from the first position to the second position bythe electrostatic force generating part.
 4. The optical switch of claim3, wherein an anti-electrostatic electrode, which serves to prevent anelectrostatic force from being generated between the rotating mirror andthe substrate, is formed at around a sidewall of the electrostatic forcegenerating part contacting the rotating mirror and under the rotatingmirror.
 5. The optical switch of claim 2, wherein a spring, which servesto prevent the first and second input fibers and the first and secondoutput fibers from separating from the trenches, is formed over thetrenches.
 6. The optical switch of claim 5, wherein the spring is formedof a material the rotating mirror is formed of.
 7. The optical switch ofclaim 2, wherein an anti-electrostatic electrode, which serves toprevent an electrostatic force from being generated between the rotatingmirror and the substrate, is formed at around a sidewall of theelectrostatic force generating part contacting the rotating mirror andunder the rotating mirror.
 8. The optical switch of claim 1, wherein therotating mirror has a first position where the rotating mirror issubstantially parallel with the substrate and a second position wherethe rotating mirror is substantially perpendicular to the substrate, andturns from the first position to the second position by theelectrostatic force generating part.
 9. The optical switch of claim 8,wherein an anti-electrostatic electrode, which serves to prevent anelectrostatic force from being generated between the rotating mirror andthe substrate, is formed at around a sidewall of the electrostatic forcegenerating part contacting the rotating mirror and under the rotatingmirror.
 10. The optical switch of claim 8, wherein a first incidentlight beam from the first input fiber is deflected to the second outputfiber and a second incident light beam from the second input fiber isdeflected to the first output fiber when the rotating mirror is at thesecond position.
 11. The optical switch of claim 1, wherein ananti-electrostatic electrode, which serves to prevent an electrostaticforce from being generated between the rotating mirror and thesubstrate, is formed at around a sidewall of the electrostatic forcegenerating part contacting the rotating mirror and under the rotatingmirror.
 12. The optical switch of claim 1, wherein the first opticalpath is substantially orthogonal to the second optical path.
 13. Theoptical switch of claim 1, wherein the bars are torsion bars.
 14. Anoptical switch comprising: a substrate; a first light input path and afirst light output path that are substantially coaxially disposed at apredetermined distance apart in a first optical path; a second lightinput path and a second light output path that are substantiallycoaxially disposed at a predetermined distance apart in a second opticalpath, wherein the first optical path and the second optical pathintersect at about a central point; means for changing the first opticalpath of a first incident light beam from the first light input path andthe second optical path of a second incident light beam from the secondlight input path, wherein the means for changing the first and secondoptical paths is rotatively supported at about the central point on thesubstrate; and an electrostatic force generating part that supplies adrive force to the means for changing the first and second opticalpaths.
 15. The optical switch of claim 14, wherein the means forchanging the first and second optical paths deflects the first incidentlight beam to the second light output path and the second incident lightbeam to the first light output path.